Drilling a wellbore within a subterranean formation generally involves drilling through different regions, or strata, of the subterranean formation that may vary in structure and/or composition. As such, interactions between a drilling assembly and the wellbore may vary with the stratum that is being drilled. In addition, different strata of the subterranean formation may respond differently to the drilling process.
As an example, certain (relatively harder) strata of the subterranean formation may have a higher strength and/or may resist the drilling process more than other (relatively softer) strata of the subterranean formation. As another example, a drilling process that may be effective at drilling a first stratum of the subterranean formation may be ineffective or less effective at drilling a second stratum of the subterranean formation and/or may damage the second stratum of the subterranean formation.
As yet another example, interface regions between two different strata of the subterranean formation may present distinct challenges to the drilling process. As an example, the drilling assembly may stick within the interface region. In extreme situations, this sticking may lead to loss of the drilling assembly within the wellbore and/or may require expensive and/or time-consuming mitigation processes to release the stuck drilling assembly from the wellbore. As another example, one or more of the strata may fracture if the drilling process is not carefully regulated within the interface region. This fracturing may permit drilling fluid to flow away from the wellbore, leading to lost returns, a potential loss of hydrostatic pressure, which may result in well control related issues, and/or further damage to the subterranean formation.
In subterranean formations that include few interface regions, the drilling process may be optimized for drilling in each strata, and the potential for loss of the drilling assembly and/or fracture of strata may be relatively low. However, in subterranean formations that include a high number of interface regions, that include rapid changes between differing strata, and/or that include a high spatial frequency of interface regions, the potential for loss of the drilling assembly and/or fracture of the strata may increase substantially. Such subterranean formations may be referred to herein as “cloudy” formations.
When drilling a wellbore within cloudy formations and/or within cloudy portion(s) of a subterranean formation, it may be desirable to modify one or more parameters of the drilling process. Additionally or alternatively, it also may be desirable to predict the presence and/or location of cloudy formations and/or of cloudy portion(s) of the given subterranean formation. Thus there exists a need for improved systems and methods for characterizing a spatial frequency of interface regions within a subterranean formation.